Method for preparing water-soluble acrylic copolymers

ABSTRACT

The invention concerns a method for preparing water-soluble acrylic copolymers comprising the following steps: (i) preparing at least a monomer (1) of formula (I) wherein Ao is a —(RtO) m Rz or —NRp (RtO) m Rz group, by reacting a (meth)acrylic anhydride derivative (1′) of formula (II) with a compound of formula AoH, Ao being as defined above; (ii) copolymerizing said monomer (1) with at least a monomer (2) of (meth)acrylic acid or of a derivative of said acid. The invention also concerns novel water-soluble acrylic copolymers and their use as superplasticizers or dispersants for hydraulic binders such as cements.

The present invention relates to a process for the preparation ofwater-soluble acrylic copolymers and to water-soluble acryliccopolymers, and to their use as plasticizers or dispersants forhydraulic binders, such as cements.

The use of plasticizers or dispersants in suspensions or pastes ofhydraulic inorganic binders is well known.

Much research is constantly being carried out to develop novelplasticizers or dispersants which make it possible to improve theTheological characteristics of cement compositions, for the purpose ofavoiding recourse to the addition of water to compensate for the declinein rheological characteristics with time.

Thus, the European patent application published under the number 753 488relates to a cement dispersant obtained by polymerization in thepresence of a chain-transfer agent. To obtain the desired molecular massdistribution, use is made, as chain-transfer agent, of an alcohol or acarboxylic acid comprising a thiol group. However, cement suspensionscomprising such a dispersant are unsatisfactory with regard to theirrheological and mechanical properties.

The European patent application published under the number 799 807relates to a process for dispersing a cement composition in which use ismade of a polymer obtained by polymerization of a monomer componentcomprising a monomer of alkoxypoly(alkylene glycol)mono(meth)acrylicester type produced by an inter-esterification reaction. Thedisadvantage of such a preparation is that it leads to the formation ofby-products of the di(meth)acrylic functional ester type, which resultsin crosslinking during the polymerization and produces a crosslinkedmacromolecular polymer which is not very effective as cement dispersingagent.

The European patent application published under the number 976 769provides acrylic copolymers comprising the following repeat units:—[CR_(a)R_(c)—CR_(b)COO⁻M⁺]- and —[CR_(i)R_(iii)—CR_(ii)(CH₂)_(n)Ao]-in which

-   -   R_(a), R_(b), R_(c), R_(i) and R_(ii) are identical or different        and represent a hydrogen atom or a methyl group; M⁺ is a proton        or a cation of an element from Group IA or IIA or an ammonium; n        is an integer between 0 and 2; Ao is —COO—(R_(T)O)_(m)—R_(z),        where R_(T) is a saturated C₂ to C₄ alkyl group, m is an integer        between 7 and 50 and R_(z) is a hydrogen atom or a C₁ to C₄        alkyl group; and R_(iii) is a hydrogen atom or the COOH group,        COO⁻M⁺ group in which M⁺ is as defined above or Ao group as        defined above;    -   these copolymers optionally comprising a third type of repeat        unit in an amount of between 0 and 20% with respect to the total        mass of the repeat units.

These copolymers, which comprise silanol groups in the end position, areobtained by copolymerization of the monomers in the presence of thefollowing chain-transfer agents:

-   -   (A) SH—R_(o)—Si(R_(IB))_(NB)(OR_(IA))_(NA), in which R_(IA) is a        hydrogen or a saturated C₁ to C₃ alkyl, R_(IB) is a C₁ to C₃        alkyl, NB is an integer having the value 1 or 0, NA is an        integer having the value 2 or 3, and R_(o) is a linear or        branched alkylene chain having from 1 to 20 carbon atoms;        -   or a mixture of (A) with inorganic phosphorous or phosphoric            acids or their salts.

Such copolymers exhibit advantageous properties as regards thedispersion of cement. However, because the control of their molecularmass is obtained by means of the chain-transfer agent, during their use,their structure is frozen, it does not change with time and does notdevelop according to the alkaline nature of the medium.

A subject matter of European patent application No. 747 374 is ahydrophilic contact lens formed by copolymerization of a polymerizablemixture comprising at least one hydrophilic monomer and additionallycomprising at least one crosslinking agent; mention is made, as exampleof such a crosslinking agent, of polyethylene glycol having, at its twoterminal ends, acrylate or methacrylate groups.

A subject matter of the invention is therefore the preparation ofwater-soluble acrylic copolymers not exhibiting the disadvantages whichhave just been mentioned.

A first subject matter of the invention is therefore a process for thepreparation of a water-soluble acrylic copolymer comprising thefollowing stages:

-   -   (i) preparation of at least one monomer (1) of formula    -    in which        -   R₁, R₂ and R₃ are identical to or different from one another            and can be a hydrogen atom or a methyl group;        -   Ao is an —O(RtO)_(m)Rz or —NRp(RtO)_(m)Rz group, Rt being a            saturated alkylene group having from 1 to 4 carbon atoms, Rz            being a saturated alkyl group having from 1 to 6 carbon            atoms and Rp being a hydrogen atom or a saturated alkyl            group having from 1 to 8 carbon atoms;        -   by reaction of a (meth)acrylic anhydride derivative (1′) of            formula        -    in which R₁, R₂ and R₃ are as defined above,        -   with a compound of formula AoH, Ao being as defined above,    -   (ii) copolymerization of said monomer (1) with at least one        monomer (2) of (meth)acrylic acid or of a derivative of this        acid.

A second subject matter of the invention relates to a water-solubleacrylic copolymer capable of being obtained by a process comprising thefollowing stages:

-   -   (i) reaction of:        -   a compound of formula AoH, in which:        -   Ao is an —O(RtO)_(m)Rz or —NRp(RtO)_(m)Rz group, Rt being a            saturated alkylene group having from 1 to 4 carbon atoms, m            being an integer between 3 and 150, Rz being a saturated            alkyl group having from 1 to 6 carbon atoms and Rp being a            hydrogen atom or a saturated alkyl group having from 1 to 8            carbon atoms; with        -   an excess of a (meth)acrylic anhydride derivative (1′) of            formula        -    in which R₁, R₂ and R₃ are identical to or different from            one another and can be a hydrogen atom or a methyl group;    -   (ii) optionally, partial or complete neutralization, by neutral        or basic hydrolysis, of the excess of the unreacted derivative        (1′);    -   (iii) copolymerization of the product obtained in stage (ii)        with at least one monomer (2) of (meth)acrylic acid or of a        derivative of this acid;        -   provided that, if complete neutralization in stage (ii) is            chosen, then a derivative (1)′ is chosen such that its            neutralized form is different from the monomer (2).

A third subject matter of the invention relates to the use of acopolymer according to the invention or obtained by the processaccording to the invention as plasticizer or dispersant in a hydraulicbinder.

A fourth subject matter of the invention is a hydraulic bindercomposition comprising at least one copolymer according to the inventionor obtained by the process according to the invention.

A fifth subject matter of the invention is an aqueous solutioncomprising at least one copolymer according to the invention or obtainedby the process according to the invention.

Thus, the invention introduces the following advantages:

-   -   it makes available acrylic copolymers which are not very        crosslinked or are entirely uncrosslinked, which makes it        possible to avoid the gelling phenomena which render them        unsuitable for numerous applications;    -   it makes it possible to prepare acrylic copolymers with highly        varied structures, because of the highly variable lengths of the        polyoxyalkylated chains and monomer ratios which can be used,    -   it makes it possible to prepare aqueous solutions comprising a        high concentration of acrylic copolymer;    -   it makes it possible to cheaply obtain copolymers with improved        properties with respect to those of the comparable compounds of        the state of the art;    -   it thus makes it possible to reduce the cost of the hydraulic        binder compositions and to improve the mechanical properties of        these compositions after curing.

Other characteristics and advantages of the invention will now bedescribed in detail in the account which follows.

Preparation of the Monomer (1) (Meth)acrylic Anhydride Derivative (1′)

The (meth)acrylic anhydride derivative (1′) is preferably acrylicanhydride or methacrylic anhydride, which are prepared, for example, byreaction of (meth)acrylic acid with acetic anhydride in the presence ofa polymerization inhibitor.

This reaction is disclosed in particular in the French patentapplication published under the number 2 592 040, Of course, theprocedure disclosed in this document can be adapted by a person skilledin the art so that it makes possible the preparation of the derivative(1′) in which one and/or the other of the R₁ and R₃ groups is a (are)methyl group(s).

Compound AoH

According to the invention, the compound AoH can be either a compound offormula HO(RtO)_(m)Rz or a compound of formula HNRp(RtO)_(m)Rz.

Mention may be made, as examples of compounds of formula HO(RtO)_(m)Rz,of:

-   -   methoxy(polyethylene glycol), methoxy(polypropylene glycol),        methoxy(polyethylene glycol)(polypropylene glycol),        methoxy(polyethylene glycol)(polybutylene glycol),        methoxy(polypropylene glycol)(polybutylene glycol),        methoxy(polyethylene glycol)(polypropylene glycol)(polybutylene        glycol),    -   ethoxy(polyethylene glycol), ethoxy(polypropylene glycol),        ethoxy(polyethylene glycol)(polypropylene glycol),        ethoxy(polyethylene glycol)(polybutylene glycol),        ethoxy(polypropylene glycol)(polybutylene glycol),        ethoxy(polyethylene glycol)(polypropylene glycol)(polybutylene        glycol),    -   butoxy(polyethylene glycol), butoxy(polypropylene glycol),        butoxy(polyethylene glycol)(polypropylene glycol),        butoxy(polyethylene glycol)(polybutylene glycol),        butoxy(polypropylene glycol)(polybutylene glycol) and        butoxy(polyethylene glycol)(polypropylene glycol)(polybutylene        glycol).

Mention may be made, as examples of compounds of formulaHNRp(RtO)_(m)Rz, of:

-   -   methoxy(polyethylene glycol)amine, methoxy(polypropylene        glycol)amine, methoxy(polyethylene glycol)(polypropylene        glycol)amine, methoxy(polyethylene glycol)(polybutylene        glycol)amine, methoxy(polypropylene glycol)(polybutylene        glycol)amine, methoxy(polyethylene glycol)(polypropylene        glycol)-(polybutylene glycol)amine,    -   methoxy(polyethylene glycol)methylamine, methoxy(polypropylene        glycol)methylamine, methoxy(polyethylene glycol)(polypropylene        glycol)methylamine, methoxy(polyethylene glycol)(poly-butylene        glycol)methylamine, methoxy(polypropylene glycol)(polybutylene        glycol)methylamine, methoxy(polyethylene glycol)(polypropylene        glycol)(polybutylene glycol)methylamine,    -   methoxy(polyethylene glycol)ethylamine, methoxy(polypropylene        glycol)ethylamine, methoxy(polyethylene glycol)(polypropylene        glycol)-ethylamine, methoxy(polyethylene glycol)(polybutylene        glycol)ethylamine, methoxy(polypropylene glycol)(polybutylene        glycol)ethylamine, methoxy(polyethylene glycol)(polypropylene        glycol)(polybutylene glycol)-ethylamine,    -   ethoxy(polyethylene glycol)amine, ethoxy(polypropylene        glycol)amine, ethoxy(polyethylene glycol)(polypropylene        glycol)amine, ethoxy(polyethylene glycol)(polybutylene        glycol)amine, ethoxy(polypropylene glycol)(polybutylene        glycol)amine, ethoxy(polyethylene glycol)(polypropylene        glycol)(polybutylene glycol)-amine,    -   ethoxy(polyethylene glycol)methylamine, ethoxy(polypropylene        glycol)methylamine, ethoxy(polyethylene glycol)(polypropylene        glycol)methylamine, ethoxy(polyethylene glycol)(polybutylene        glycol)methylamine, ethoxy(polypropylene glycol)(polybutylene        glycol)methylamine, ethoxy(polyethylene glycol)(polypropylene        glycol)(polybutylene glycol)methylamine, ethoxy(polyethylene        glycol)ethylamine,    -   ethoxy(polypropylene glycol)ethylamine, ethoxy(polyethylene        glycol)(polypropylene glycol)ethylamine, ethoxy(polyethylene        glycol)(polybutylene glycol)ethylamine, ethoxy(polypropylene        glycol)-(polybutylene glycol)ethylamine, ethoxy(polyethylene        glycol)(polypropylene glycol)(polybutylene glycol)-ethylamine,    -   butoxy(polyethylene glycol)amine, butoxy(polypropylene        glycol)amine, butoxy(polyethylene glycol)(polypropylene        glycol)amine, butoxy(polyethylene glycol)(polybutylene        glycol)amine, butoxy(polypropylene glycol)(polybutylene        glycol)amine, butoxy(polyethylene glycol)(polypropylene        glycol)(polybutylene glycol)amine,    -   butoxy (polyethylene glycol) methylamine, butoxy (polypropylene        glycol)methylamine, butoxy(polyethylene glycol)(polypropylene        glycol)methylamine, butoxy(polyethylene glycol)(polybutylene        glycol)methylamine, butoxy(polypropylene glycol)(polybutylene        glycol)methylamine, butoxy(polyethylene glycol)(polypropylene        glycol)(polybutylene glycol)methylamine,    -   butoxy(polyethylene glycol)ethylamine, butoxy(polypropylene        glycol)ethylamine, butoxy(polyethylene glycol)(polypropylene        glycol)ethylamine, butoxy(polyethylene glycol)(polybutylene        glycol)ethylamine, butoxy(polypropylene glycol)(polybutylene        glycol)-ethylamine and butoxy(polyethylene        glycol)-(polypropylene glycol)(polybutylene glycol)ethylamine.    -   m is an integer which is generally between 3 and 150.

Use is preferably made of the compounds AoH in which m is greater than10 and in particular greater than 20.

Of course, use may be made of a single AoH derivative or of a mixture ofAoH derivatives.

Reaction of the Derivative (1′) with the Compound AoH

The French patent application published under the number 2 739 850 givesan example of the preparation of a monomer (1) in which Ao is an—O(RtO)_(m)Rz group, namely by reaction of a (meth)acrylic anhydridewith an alcohol of formula R⁴[OC₂H₃(R⁵)]_(n)OH, R⁴ being a hydrophobicradical and R⁵ a hydrogen atom or a methyl group.

More generally, the reaction of the derivative (1′) with the compoundAoH, whether the latter is an —O(RtO)_(m)Rz or —NRp(RtO)_(m)Rz group, isusually carried out at a temperature of between 20 and 120° C.,preferably between 30 and 100° C. The duration of the reaction dependson the experimental conditions, such as the temperature and the amountsof catalyst used, but it is usually between 1 and 20 hours. Thereactants are used in a molar ratio of the (meth)acrylic anhydridederivative (1′) to the compound AoH of between 0.6 and 3, preferablybetween 1.1 and 3. It is preferable to use at least one polymerizationinhibitor, such as hydroquinone or one of its derivatives (for exampleMeHQ), phenol derivatives, such as BHT(2,6-di(tert-butyl)hydroxytoluene), or phenothiazine. The content ofinhibitor(s) is generally between 100 and 5,000 ppm. These inhibitorsare generally used in the presence of a stream of air into the reactor.

The reaction is preferably carried out by introducing the reactants intothe reactor at a temperature appropriate for the initiation of thereaction in the liquid phase. Stirring of the mixture is then continuedat the reaction temperature for the time necessary to bring theesterification or the amidation to completion.

On completion of the reaction, the mixture of monomers obtained iscomposed of an alkoxy(polyalkylene glycol)(meth)acrylic ester monomerand/or of an alkoxy(polyalkylene glycol)(meth)acrylamide monomer.

According to a first method of preparation of the monomer (1), theexcess of the derivative (1′) remaining after the reaction between thederivative (1′) and the compound of formula AoH is completelyneutralized by neutral or basic hydrolysis before the copolymerizationof stage (ii).

The neutralization is then generally carried out by addition of water orof alkaline solution to the reaction mixture at a temperature of between50 and 80° C. for 5 to 8 hours.

According to a second method of preparation of the monomer (1), theexcess of derivative (1′) remaining after the reaction between thisderivative and the compound of formula AoH is left during thecopolymerization stage (ii) or is neutralized, but only in part, beforethis stage.

It is desirable for the level of unreacted derivative (1′) to remainless than or equal to 20% with respect to the starting amount ofderivative (1′) introduced. Neutralization is therefore preferable whenthe level of unreacted derivative (1′) is greater than 20%.

The inventors have discovered that, surprisingly, the presence of anexcess of (meth)acrylic anhydride derivative (1′) advantageously resultsin the production of superplasticizers having good rheological andprocessing properties because of their ability to gradually releaselinear active chains.

A probable explanation of this phenomenon is that complex copolymernetworks are formed when the derivative (1′) has not been neutralized orhas been partially neutralized before the copolymerization stage. Thesenetworks are subsequently destroyed by the basicity of the hydraulicbinder, which results in the generation of new linear chains whichinteract with the cement particles and thus modify their electrostaticand steric properties. The rate of generation of the linear chainsproduces an effect equivalent to the constant addition of linearpolymers to the hydraulic binder. The more complex the network, thegreater the “reservoir” of linear chains. The ratio of the free linearchains to the trapped linear chains can be adjusted by an appropriatechoice of the amount of derivative (1′). It is possible in this way toobtain the desired activity of the copolymer. It is also possible toblend copolymers obtained with the neutralized derivative (1′) withcopolymers obtained with the unneutralized or only slightly neutralizedderivative (1′).

This possibility of preparing a “made to measure” copolymer is a majorinnovation with respect to the techniques of the prior art.

The partial neutralization is carried out as for the first embodiment,that is to say that water or an alkaline solution is added as indicatedfor the first method of preparation. By adjusting the amount of wateradded, it is possible to obtain an aqueous solution comprising a mixtureof monomers, the concentrations of which and the concentration ofhydrolyzed derivative (1′) correspond to the concentrations desired forthe following copolymerization stage.

This preparation of monomers (1), whether they are in the ester form orin the amide form, thus makes it possible to prepare a mixture ofmonomers which, first, is appropriate for the copolymerization stage andwhich, secondly and in contrast to the techniques of the prior art, doesnot require any distillation operation. This therefore constitutes amarked improvement with respect to the prior art.

Monomer (2)

The monomer (2) can correspond to the formula:

in which

-   -   R_(a), R_(b) and R_(c) are identical to or different from one        another and can be a hydrogen atom or a methyl group;    -   M′ is a hydrogen atom, a metal from Group IA or IIA, an ammonium        or an organic amine group.

Mention may be made, as examples of monomers (2), of acrylic acid,methacrylic acid, their salts with alkali metals or alkaline earthmetals, their ammonium salts and their organic amine salts. Mixtures ofthese compounds may be used.

Preferably, acrylic acid or methacrylic acid is used as monomer (2).

Copolymerization

The copolymerization is generally carried out with a ratio by weight ofthe monomer (1) to the monomer (2) of between 5:95 and 98:2, preferablybetween 50:50 and 98:2.

The copolymerization of stage (ii) can be carried out in the presence ofat least one other monomer (3) which is a monomer copolymerizable withthe monomers (1) and (2).

The proportion by mass of this monomer (3) is generally between 0 and20% with respect to the total mass of the monomers (1), (2) and (3).

Use may be made, as monomers (3), of the monomers mentioned on page 5,lines 49 to 58, of the abovementioned European patent application No.753 488, those mentioned on page 7, lines 12 to 26, of theabovementioned European patent application No. 7990807 or thosementioned on page 10, line 37, to page 12, line 3, of the internationalpatent application published under the number WO 98/28353.

Use is preferably made of one or more monomers (3) chosen from:

-   -   (meth)acrylic anhydride,    -   (meth)acrylic esters of C₁ to C₂₀ aliphatic alcohols, maleic        acid or its anhydride and their derivatives (salts, hemiesters        or esters of alcohols with a long polyoxyalkylated chain,        alkoxyalcohols, amides or semiamides with a long        polyoxyalkylated amine chain),    -   polyethoxy monoallyl ethers of formula CH₂═CHCH₂O(C₂H₄O)_(p)—R,        in which p is between 5 and 100 and R is a C₁ to C₄ alkyl,    -   monounsaturated C₃ to C₅ sulfonic acids, and    -   compounds of formula CH₂═CR_(X)—CO-A-CR_(X1)—CH₂R_(X2)—SO₃M′, in        which M′ is as defined for the monomer (2), R_(X) is a hydrogen        atom or a methyl, R_(X1) and R_(X2) are, independently of one        another, a hydrogen atom or a C₁ to C₈ alkyl, and A is NH or        N—CH₃.

The copolymerization of the monomers (1), (2) and, if appropriate, (3)is generally carried out in water, although short-chain alcohols, suchas methanol, ethanol or isopropyl alcohol, or other solvents, such asmethyl ethyl ketone, may also be suitable.

The process may be continuous, semicontinuous or batchwise. It is alsopossible to carry out the copolymerization in the same reactor as thatwhere the monomer (1) was prepared. In this way, changing of the reactoris avoided, which constitutes an additional advantage of the invention.In this case, it may be desirable to adjust the mixture of monomers inorder for the molar ratios of the monomers to be those which aredesired.

For the purpose of initiating the copolymerization reaction, it ispreferable to add an appropriate free-radical reaction initiator to themixture of monomers, in the bulk form or in solution in water or in asolvent. If the copolymerization is carried out in water or in analcohol medium, use is preferably made of water-soluble copolymerizationinitiators, such as ammonium, sodium or potassium persulfate, orhydrogen peroxide, with or without an activator, such as FeSO₄.7H₂O orsodium metabisulfite, and purging the reactor with nitrogen.

In the case of the use of polar solvents not comprising hydroxyl groups,it is convenient to use initiators which are soluble in the same medium,such as a hydroperoxide, ketone peroxides or percarbonates.

For the purpose of controlling the molecular mass of the polymersobtained, use may be made of a chain-transfer agent.

Use may be made, as chain-transfer agent, of derivatives of thiol type.

Mention may be made, as derivatives of thiol type, of those mentioned onpage 5, lines 41 to 48, of the abovementioned European patentapplication No. 799 807, in particular mercaptoethanol, thioglycerol,thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid,thiomalic acid, octyl thioglycolate, octyl 3-mercaptopropionate or2-mercaptoethanesulfonic acid. Of course, these agents can be used aloneor as a mixture.

Use is preferably made of the chain-transfer agents of thiol typedisclosed in the abovementioned European patent application No. 976 769,which are functionalizing chain-transfer agents of formulaHS—Ro-Si—(OR_(1a)) in which R_(1a) is H or a saturated C₁ to C₃ alkylgroup and Ro is a linear or branched alkyl chain. These agents are usedas such or as a mixture with H₃PO₂, H₃PO₃ or their salts. They arepreferred because they introduce end polar groups (silanols) whichimprove the ability of the copolymer to become firmly attached to theinorganic particles.

Mercaptopropyltrimethoxysilane is a particularly advantageouschain-transfer agent.

The reaction temperature can vary according to the type of solvent used.In the case of an aqueous-phase copolymerization, the temperatures aregenerally within the range from 50 to 120° C., preferably from 60 to100° C. The reaction duration is generally between 1 and 8 hours,preferably between 2 and 5 hours. The content of dry matter in theaqueous polymer solution can vary between 20 and 70% by weight; it ispreferably between 30 and 60%.

A small amount of water can be run into the reactor before the additionof the reactants. The reactants can be introduced simultaneously at aconstant flow rate with stirring.

The initiator can be added separately.

As indicated above, the optional neutralization stage can also be takeplace at the end of the copolymerization reaction, during the cooling.

As mentioned above, the reaction can be carried out batchwise,preferably in the reactor which has been used for the preparation of themonomer (1), by mixing the monomers already present in the reactor withthe other monomer or monomers, if desired, before the beginning of thecopolymerization.

According to an alternative form, the copolymer is partially orcompletely neutralized during its formation by simultaneous (butseparate) introduction of an alkaline solution during the introductionof the mixture of monomers into the reactor.

The amount of alkaline solution introduced is preferably calculated inorder for the neutralization to be only partial and more preferably suchthat the amount of copolymer neutralized is between 40 to 70%.

According to another alternative form, the acrylic copolymer ispartially or completely neutralized after the copolymerization stage.The copolymer is then preferably neutralized so that its pH is between 4and 9.

Use

When the polymers according to the invention are added to an aqueouscement suspension, they improve both the mixing and the dispersion ofthe mass of cement and its rheological properties while being betterplasticizers than the plasticizers of the prior art.

According to their structure, it is possible to improve one or more oftheir effects, which are, in particular, the prolongation of therheology, the reduction in water, the curing or the setting delay, andthe self-leveling nature of the cement suspension. These effects arealso observed during use with other hydraulic binders, such as clays forthe ceramic industry, mortars and plasters.

The aqueous mixtures in the form of suspensions or pastes comprising thecement and copolymers according to the invention comprise an amount ofcopolymer generally of between 0.03 and 2%, preferably between 0.05 and1%, by weight of copolymer with respect to the dry cement.

The addition of the copolymers according to the invention to the cementsuspensions or pastes is carried out by introduction of the copolymersas such or in the form of an aqueous solution comprising, by weight,more than 25% and preferably more than 30% of copolymer. Mixing issubsequently carried out until the mass becomes homogeneous.

When the polymer solution is added to a cement suspension or acement-based paste, the volume of water is preferably reduced by theamount of water present in the polymer solution, so as to maintain thedesired water/cement ratio.

Another advantage provided by the invention is that, as aqueoussolutions which can comprise more than 50% of polymer can be producedreproducibly and routinely, these solutions can be sprayed usingconventional equipment and according to conventional and inexpensiveprocesses.

Additives

In addition to the plasticizers according to the invention, the cementcomposition can comprise conventional additives, such as air-entrainingagents, antifoams, thickening agents, wetting agents, expanders, setretarders or accelerators, or shrinkage reducers. It is also possible tointroduce conventional cement dispersants, such as dispersants based onpolycondensates of sulfonated melamine or of sulfonated naphthalene andof formaldehyde, or else lignin derivatives.

EXAMPLES

The following examples are given solely by way of illustration: theyhave no limiting nature.

Measurement Methods Used a) Slump Test with an Abrams Cone According toNF 18-451

A concrete with the following composition is used:

Gravel 10/20 R GEM 830 kg Gravel 4/10 R GEM 308 kg Sand 0/4 R GEM 750 kgCPA-CEMI 42.5 R Altkirch 300 kg

The concrete is mixed for 30 seconds before each of the tests and thenit is reintroduced into the remainder of the cement suspension. Thetrapped air measurement is carried out on the fresh concrete at 10minutes according to NFP 18-353.

The test specimens for the determination of the mechanical propertiesare 15×15×15 cm cubes prepared at the time t=0 in a suspension differentfrom that which is used for the rheological measurements. Monitoring ofthe compressive strength is carried out at 24 h, 7 days and 28 daysaccording to Standard NFP 18-406.

b) Determination of the Absolute Viscosity

The viscosity is determined at 30 revolutions per minute (No. 2 spindle)on a Brookfield LVT2 viscometer at a temperature of 25° C. or with aRheology International viscometer, model R1:2: M, spindle 2.

c) Determination of the Molecular Mass by Liquid Chromatography

The polymer is dissolved, at a concentration of 1% (weight/volume) (40mg/4 ml), in an aqueous NH₄OH solution containing NaN₃ at aconcentration of 0.02%. The liquid chromatography apparatus is composedof a Constometric® 3200 pump, a Rheodine® 7125 valve, a DifferentialRefractometer R 401® detector, a PW 2000-4000 TSK® gel column connectedin series and thermostatically controlled at 40° C., and a SpectraPhysics® integrator.

The columns are calibrated with polyethylene glycols of variablemolecular mass and 200 μl of sample solution are injected using 1%(weight/volume) dioxane in water as reference. The molecular mass of thepolymer is determined according to the maximum of the elution peak.

d) Minislump Test

An Erweka AR 400 mixer is used to prepare the following composition:

Portland cement, CPA-CEMI 42.5 625 g Sand, standardized, EN-196-1 1 350g Silica, Milisil ® SA 4 (Silbeco Italiana) 50 g Water (water/cementratio 0.42) 261 g Amount (in grams) of 35% weight/weight polymer 3.2 gsolution (weight of polymer/weight of cement ratio of 0.175%)

If the concentration of polymer is different from 35%, the amount ofsolution added to the cement is consequently adjusted in order for thepolymer/cement ratio to meet the condition given (0.175%). Thedifferences in water content are compensated for by adjusting the totalamount of water in order to observe the required water/cement ratio.

First, the polymer solution is diluted with a certain amount (5-10 ml)of the total amount of water used. The water is poured into the vessel(251-256 ml) and, with mechanical stirring (20 revolutions/minute) andin this order, the cement with the silica, then, portionwise, the sandand, at the end, the polymer solution of the present invention areadded.

Stirring is continued for 1 minute at the same speed and for anadditional minute at 30 revolutions/minute. Stirring is subsequentlyhalted while pouring the homogeneous mass into a brass circulartruncated cone with open ends, with a height of 40 mm, a diameter of theupper surface of 70 mm and a diameter of the surface of the base of 80mm, placed on a PVC sheet. This container must be filled from the baseto the brim. The excess suspension is removed using a strip. Twomeasurements are carried out:

-   -   1) the truncated cone is filled and, after one minute, the        contents are poured onto the sheet by lifting up the truncated        cone;    -   2) the truncated cone is filled a second time with the same        suspension, after having allowed the latter to stand for        variable times (2, 4 and 6 hours) and having remixed it manually        before the test, and the operation of part 1) is repeated.        Thirty seconds after lifting up the truncated cone, the diameter        of the paste obtained is measured in centimeters.

Example 1 Preparation of an alkoxy(polyalkylene glycol) methacrylicester

The apparatus consists of a 2 liter glass reactor equipped with aheating jacket connected to a thermostatically-controlled bath, equippedwith a thermocouple, with a stirrer, with a feed pump, with a droppingfunnel and with a condenser.

The following are introduced with stirring into the reactor, which hasbeen preheated to 80° C.: 500 g (0.5 mol) of molten MPEG 1000(methoxy(polyethylene glycol) with an average molecular mass of 1 000g/mol); 88.5 g (0.57 mol) of methacrylic anhydride; 0.6 g of BHT(3,5-di(tert-butyl)-4-hydroxytoluene) stabilizer; and 5 g oftriethylamine as catalyst.

The reaction is carried out at 80° C. for 6 hours; subsequently, 175 gof water are added and the hydrolysis of the anhydride is brought tocompletion by stirring the reaction mixture at 80° C. for 5 hours. The70% solution is further diluted with 280 g of water to a final contentof ester of approximately 50%.

Example 2 Preparation of an alkoxy(polyalkylene glycol) methacrylicester

The following are introduced with stirring into the same reactor as inexample 1, which has been heated beforehand to 80° C.: 500 g (0.25 mol)of molten MPEG 2000 (methoxy(polyethylene glycol) with an averagemolecular mass of 2 000); 44.3 g (0.29 mol) of methacrylic anhydride;0.6 g of BHT (3,5-di(tert-butyl)-4-hydroxytoluene) as stabilizer; and 5g of triethylamine as catalyst.

The reaction is carried out at 80° C. for 7 hours, then 254 g of waterare added and the hydrolysis of the anhydride is brought to completionby stirring the reaction mixture at 80° C. for 5 hours. After cooling,an additional 245 g of water are added to achieve a concentration of theester in water of approximately 50%.

Example 3 Preparation of an alkoxy(polyalkylene glycol)methacrylamide

The following are added with stirring to the same reactor as in example1, which has been heated beforehand to 80° C.: 500 g (0.5 mol) of moltenJeffamine® M 1000 (methoxy(polyethylene glycol)(polypropyleneglycol)monoamine with an average molecular mass of 1 000 g/mol); 88.5 g(0.57 mol) of methacrylic anhydride; and 0.6 g of BHT(3,5-di(tert-butyl)-4-hydroxytoluene) stabilizer.

The reaction is carried out at 80° C. for 4 hours, then 400 g of waterare added and the reaction is continued at 80° C. for an additional 3hours. The final mixture, comprising approximately 50% of amide, iscooled and is used in the following copolymerization operation.

Example 4 Preparation of the alkoxy(polyalkylene glycol)methacrylamide

The following are introduced with stirring into the same reactor as inexample 1, which has been heated beforehand to 80° C.: 400 g (0.19 mol)of molten Jeffamine® M 2070 (methoxy(polyethylene glycol)(polypropyleneglycol)monoamine with an average molecular mass of 2 070); 34.2 g (0.22mol) of methacrylic anhydride; and 0.5 g of BHT(3,5-di(tert-butyl)-4-hydroxytoluene) stabilizer.

The reaction is carried out at 80° C. for 4 hours, then 385 g of waterare added and the reaction is continued at 80° C. for an additional 3hours.

The final mixture, with an amide content of approximately 50%, is cooledand used in the following copolymerization operation.

Example 5 Preparation of an alkoxy(polyalkylene glycol) methacrylicester Comprising Unhydrolyzed Methacrylic Anhydride

The following are introduced with stirring into the reactor of example1, which has been preheated to 80° C.: 500 g (0.5 mol) of molten MPEG1000 methoxy(polyethylene glycol) with an average molecular mass of 1000 g/mol); 108 g (0.7 mol) of methacrylic anhydride; 0.6 g of BHT,3,5-di(tert-butyl)-4-hydroxytoluene) stabilizer; and 5 g oftriethylamine as catalyst.

The reaction is carried out at 80° C. for 6 hours; after cooling, 460 gof water are added in order to have a final content of ester ofapproximately 50%; the solution thus obtained is used immediately in thefollowing copolymerization stage.

Example 6 Preparation of an alkoxy(polyalkylene glycol) methacrylicester Comprising Unhydrolyzed Methacrylic Anhydride

The following are introduced with stirring into the reactor of example1, which has been preheated to 80° C.: 500 g (0.25 mol) of molten MPEG2000 (methoxy(polyethylene glycol) with an average molecular mass of 2000 g/mol); 62 g (0.4 mol) of methacrylic anhydride; 0.6 g of BHT(3,5-di(tert-butyl)-4hydroxytoluene) stabilizer; and 5 g oftriethylamine as catalyst.

The reaction is carried out at 80° C. for 6 hours; after cooling, 470 gof water are added in order to have a final content of ester ofapproximately 50%; the solution thus obtained is used immediately in thefollowing copolymerization stage.

Example 7 Preparation of the Dispersant According to the Invention(Copolymerization)

277 g of demineralized water are introduced with stirring into a 1 literglass reactor equipped with a thermocouple, with a stirrer, with adropping funnel, with three feed pumps, with a nitrogen inlet pipe andwith a reflux condenser, the trapped air being displaced by flushingwith nitrogen, and heating is carried out to 80-85° C. When thistemperature is reached, the following are added over three hours using apump:

-   -   an aqueous mixture formed of 400 g of an aqueous solution        prepared according to Example 1, 29.3 g of methacrylic acid; and        4.4 g of Dynasylan® MTMO (3-mercaptopropyltrimethoxysilane) as        functionalizing agent; and    -   16 g of an aqueous solution (10% weight/weight) of ammonium        persulfate (NH₄)₂S₂O₈.

After 3 hours, the reaction is brought to completion by the addition,all at once, of 4 g of a 10% weight/weight ammonium persulfate solutionand while maintaining the temperature at approximately 80° C. forapproximately 1 hour.

After cooling, the polymer solution has a content of dry matter of 35.7%(viscosity 0.15 Pa.s at 100 revolutions minute) and is virtuallycompletely neutralized with a 30% aqueous sodium hydroxide solution(final content of dry matter 34%).

The cement dispersant of the present invention has a weight-averagemolecular mass of 22 000 and a maximum value of 14 000.

The minislump test as defined above is subsequently carried out with thepolymer solution. The results are recorded below in table 1.

Example 8 Preparation of the Dispersant According to the Invention(Copolymerization)

The dispersant is prepared in a similar way to what is indicated forexample 7 but while employing 273 g of demineralized water and:

-   -   an aqueous mixture formed by 500 g of aqueous solution prepared        according to Example 2, 16.8 g of methacrylic acid; and 2.5 g of        Dynasylan® MTMO (3-mercaptopropyltrimethoxysilane) as        functionalizing agent; and    -   16 g of an aqueous solution (10% weight/weight) of ammonium        persulfate (NH₄)₂S₂O₈.

After 3 hours, the reaction is brought to completion by adding, all atonce, 4 g of a 10% weight/weight ammonium persulfate solution and whilemaintaining the temperature at 80-85° C. for approximately 1 hour.

After cooling, the polymer solution has a content of dry matter of 35.7%and is virtually completely neutralized using a 30% aqueous sodiumhydroxide solution (content of dry matter 35%).

The cement dispersant of the present invention has a weight-averagemolecular mass of 25 000 and a maximum value of 14 000.

The minislump test as defined above is subsequently carried out with thepolymer solution. The results are recorded below in table 1.

Example 9 Preparation of Cement Dispersant by Way of Comparison

A cement dispersant is prepared in a similar way to what is indicatedfor example 7 but while employing a commercially available monomerprepared by trans-esterification (Bisomer S 20 W from Inspec Ltd, whichis a 50% aqueous solution of methoxy(polyethylene glycol)methacrylatewith an average molecular mass of 2 080) and,

-   -   an aqueous mixture formed by 500 g of Bisomer 20 W, 28.9 g of        methacrylic acid, and 2.5 g of Dynasylan® MTMO        (3-mercaptopropyltrimethoxysilane) as functionalizing agent; and    -   16 g of aqueous ammonium persulfate (NH₄)₂S₂O₈ solution (10%        weight/weight).

After less than 2 hours, the reaction is halted because of completeformation of a water-insoluble, gelled and crosslinked product.

The minislump test as defined above is subsequently carried out with thepolymer solution. The results demonstrate the complete absence ofplasticizing properties of this product.

The experiment was repeated with samples of different production batchesfrom Inspec Ltd. The same negative results were obtained.

Example 10 Preparation of the Dispersant According to the Invention(Copolymerization)

The dispersant is prepared in a similar way to what is indicated forexample 7 but while employing the monomer mixture of example 3.

The reactor is charged with 390 g of demineralized water and then, afterheating to 80-85° C., the following are added:

-   -   an aqueous mixture composed of 500 g of aqueous solution        prepared according to Example 3; 32.7 g of methacrylic acid; and        5.1 g of Dynasylan® MTMO (3-mercaptopropyltrimethoxysilane) as        functionalizing agent; and    -   33.3 g of an aqueous solution (10% weight/weight) of ammonium        persulfate (NH₄)₂S₂O₈.

After 3 hours, the reaction is brought to completion by adding, all atonce, 8.3 g of a 10% weight/weight ammonium persulfate solution andwhile maintaining the temperature at 80-85° C. for approximately 1 hour.

After cooling the polymer solution, the content of dry matter is 35.2%and the polymer solution is subsequently virtually completelyneutralized using a 30% aqueous sodium hydroxide solution (final contentof dry matter 34.2%).

The cement dispersant of the present invention has a weight-averagemolecular mass of 22 000 with a maximum value of 11 000.

The minislump test as defined above is subsequently carried out with thepolymer solution. The results are recorded below in table 1.

Example 11 Preparation of the Dispersant According to the Invention(Copolymerization)

The dispersant is prepared in a similar way to what is indicated forexample 7 but while employing the monomer mixture of example 5.

277 g of demineralized water are introduced into the reactor and then,after heating to 80° C., the following are added:

-   -   a mixture formed of 400 g of aqueous solution prepared according        to example 5, 17.5 g of methacrylic acid; and 4.4 g of        Dynasylan® MTMO (3-mercaptopropyltrimethoxysilane) as        functionalizing agent; and    -   16 g of an aqueous solution (10% weight/weight) of ammonium        persulfate (NH₄)₂S₂O₈.

After 3 hours, the reaction is brought to completion by adding, all atonce, 4 g of a 10% (weight/weight) ammonium persulfate solution andwhile maintaining the temperature at 80° C. for approximately 1 hour.

After cooling, the polymer solution has a content of dry matter of 35.7%and is subsequently virtually completely neutralized using a 30% aqueoussodium hydroxide solution (final content of dry matter 34.4%).

The cement dispersant thus obtained has a weight-average molecular massof 30 000 and a maximum value of 17 000.

Example 12 Preparation of the Dispersant According to the Invention(Copolymerization)

The dispersion is prepared in a similar way to what is indicated forexample 7 but while employing the monomer mixture of example 6.

298 g of demineralized water are introduced into the reactor and then,after heating to 80° C., the following are added:

-   -   a mixture formed by 500 g of aqueous solution prepared according        to example 6, 18.6 g of methacrylic acid; and 2.5 g of        Dynasylan® MTMO (3-mercaptopropyltrimethoxysilane) as        functionalizing agent; and    -   16 g of an aqueous solution (10% weight/weight) of ammonium        persulfate (NH₄)₂S₂O₈.

After 3 hours, the reaction is terminated by adding, all at once, 4.5 gof a 10% (weight/weight) ammonium persulfate solution and whilemaintaining the temperature at 80° C. for approximately 1 hour. Aftercooling, the polymer solution has a content of dry matter of 34.4% andis virtually completely neutralized with a 30% aqueous sodium hydroxidesolution (final content of dry matter 33.0%).

The cement dispersant of the present invention has a weight molecularmass of 48 000 and a maximum value of 25 000.

The minislump test as defined above is subsequently carried out with thepolymer solution. The results are recorded below in table 1.

Example 13 Preparation of the Dispersant According to the Invention(Copolymerization)

The dispersant is prepared in a similar way to what is indicated forexample 7 but while employing the monomer mixture of example 6 and othermonomers.

262 g of demineralized water are introduced into the reactor and then,after heating to approximately 80° C., the following are addedseparately:

-   -   a mixture formed by 440 g of aqueous solution prepared according        to example 6, 16.4 g of methacrylic acid; 14.0 g of methacrylic        anhydride; and 2.2 g of Dynasylan® MTMO        (3-mercaptopropyltrimethoxysilane) as functionalizing agent; and    -   14.1 g of an aqueous solution (10% weight/weight) of ammonium        persulfate (NH₄)₂S₂O₈.

After 3 hours, the reaction is brought to completion by adding, all atonce, 4.0 g of a 10% (m/m) ammonium persulfate solution and whilemaintaining the temperature at 80° C. for approximately 1 hour.

After cooling, the polymer solution has a content of dry matter of36.0%. It is subsequently neutralized with a 30% aqueous sodiumhydroxide solution (final content of dry matter: 35%).

The cement dispersant according to the present invention has amass-average molecular mass of 118 000 and a peak value of 105 000,which shows that the methacrylic anhydride resists hydrolysis and thatsignificant crosslinking has taken place.

Example 14 Preparation of the Dispersant According to the Invention(Copolymerization)

The dispersant is prepared in a similar way to what is indicated forexample 8, except that a 10 liter reactor is used and the molar ratio ofthe monomers is changed (2:1 instead of 2.8:1).

2 565 g of demineralized water are introduced with stirring into thereactor, which has been preheated to 80° C. The following are introducedseparately using pumps:

-   -   5 000 g of an aqueous solution prepared according to example 2;    -   87 g of methacrylic acid;    -   10 g of Dynasylan® MTMO as functionalizing agent; and    -   126 g of a 10% (m/m) aqueous ammonium persulfate (NH₄)₂S₂O₈        solution.

After 3 hours, the reaction is brought to completion by adding, all atonce, 32 g of 10% (m/m) aqueous ammonium persulfate solution and whilemaintaining the temperature at 80° C. for approximately one hour.

After cooling, the polymer solution has a content of dry matter of 35%.It is subsequently virtually completely neutralized using a 30% aqueoussodium hydroxide solution (final content of dry matter: 35%).

The cement dispersant according to the present invention has amass-average molecular mass of 84 000 with peak values of 90 000 and of29 000.

The minislump test as defined above is subsequently carried out with thepolymer solution. The results are recorded below in table 1.

In this table 1, the results shown were obtained according to theprocedure of the minislump test described above and by monitoring thevariations over time of the Theological properties of the suspension.

Of course, the greater the plasticity of the mixture, the greater thediameter of the paste.

Each of the figures shown in table 1 is the mean of two separatedeterminations carried out by preparing, on each occasion, thesuspension mentioned in the procedure of the minislump test.

TABLE 1 Product of Polymer/ example cement No. ratio t = 0 t = 2 h t = 4h t = 6 h t = 8 h 7 0.175 20 cm   18 cm 17.5 cm 15 cm   11 cm 8 0.23 19cm   19 cm   19 cm 18 cm 10 0.175 19 cm 16.5 cm   14 cm 11 0.175 20 cm  19 cm 18.5 cm 17 cm   14 cm 12 0.23 20 cm   21 cm 20.5 cm 20 cm 19.5cm 13 0.23 21 cm   21 cm   20 cm 19 cm   16 cm

It is thus found that the plasticity slowly decreases over time.

The dispersant of example 14 and commercial products are compared intable 2, the comparison being obtained with slump measurements accordingto the test with an Abrams cone described above.

TABLE 2 Paste No. 1 2 3 4 Additive None Commercial Commercial Exampleproduct 1 product 2 14 (1) (2) Level of addition 0.603 0.875 0.972 (%)W/C overall ratio 0.655 0.607 0.553 0.564 Slump t0 + 5 min 20 20.5 21 21Slump t0 + 30 min 16 19 18 21 Slump t0 + 60 min 13 14.5 17 18.5 Slumpt0 + 90 min 11 14 9.5 17 Density 2.346 2.342 2.369 2.37 Mechanicalstrength 9.3 12.8 18.4 20.2 at 24 hours Mechanical strength 25 35.4 39.739.5 at 7 days Mechanical strength 34.1 42.5 46.9 44.1 at 28 days (1):Sold under the name Optima 100 (2): Sold under the name Malialim A 20

It clearly emerges that very good results in terms of maintenance ofrheology (slump) and of mechanical properties (compressive test) areobtained.

1. A process for the preparation of a water-soluble acrylic copolymercomprising the following stages: (i) preparation of at least one monomer(1) of formula

in which R₁, R₂ and R₃ are identical to or different from one anotherand can be a hydrogen atom or a methyl group; Ao is an —O(RtO)_(m)Rz or—NRp(RtO)_(m)Rz group, Rt being a saturated alkylene group having from 1to 4 carbon atoms, Rz being a saturated alkyl group having from 1 to 6carbon atoms and Rp being a hydrogen atom or a saturated alkyl grouphaving from 1 to 8 carbon atoms; and m being an integer between 3 and150; by reaction of an excess of (meth)acrylic anhydride derivative (1′)of formula

in which R₁, R₂ and R₃ are as defined above, with a compound of formulaAoH, Ao being as defined above, (ii) copolymerization of said monomer(1) with at least one monomer (2) of (meth)acrylic acid or of aderivative of this acid, with the said excess of derivative (1′)remaining after the reaction between derivative (1′) and the compoundAOH, being left during copolymerization stage ii).
 2. The process asclaimed in claim 1, in which the said excess of derivative (1′), leftduring copolymerization stage, is in the neutralized form, by neutral orbasic hydrolysis before the copolymerization of stage (ii).
 3. Theprocess as claimed in claim 1, in which the said excess of derivative(1′), left during the copolymerization stage, is partially neutralizedbefore this stage.
 4. The process as claimed in claim 3, in which theexcess of derivative (1′) not neutralized before stage (ii) isneutralized after this stage.
 5. The process as claimed in claim 1wherein, in the monomer (1), m is greater than
 10. 6. The process ofclaim 1 wherein, in the monomer (1), R₁ and R₃ are hydrogen atoms. 7.The process as claimed in claim 1 wherein the monomer (2) corresponds tothe formula:

in which R_(a), R_(b) and R_(c) are identical to or different from oneanother and can be a hydrogen atom or a methyl group; M′ is a hydrogenatom, a metal from Group IA or IIA, an ammonium or an organic aminegroup.
 8. The process of claim 1 wherein the monomer (2) is(meth)acrylic acid neutralized with a metal from Group IA or IIA.
 9. Theprocess as claimed in claim 1 wherein the ratio by weight of the monomer(1) to the monomer (2) is between 5:95 and 98:2.
 10. The process asclaimed in claim 1, wherein the copolymerization of stage (ii) iscarried out in the presence of 0 to 20%, with respect to the total massof the monomers (1), (2) and (3), of at least one other monomer (3)copolymerizable with the monomers (1) and (2).
 11. The process asclaimed in claim 1, wherein the monomer (3) is chosen from the groupconsisting of the following compounds: (meth)acrylic anhydride,(meth)acrylic esters of C₁ to C₂₀ aliphatic alcohols, maleic acid or itsanhydride and their derivatives, polyethoxy monoallyl ethers of formulaCH₂═CHCH₂O(C₂H₄O)_(p)—R, in which p is between 5 and 100 and R is a C₁to C₄ alkyl, monounsaturated C₃ to C₅ sulfonic acids, and compounds offormula CH₂═CR_(x)—CO-A-CR_(x1)—CH₂R_(x2)—SO₃M, in which M is as definedfor the monomer (2), Rx is a hydrogen atom or a methyl, R_(x1) andR_(x2) are, independently of one another, a hydrogen atom or a C₁ to C₈alkyl, and A is NH or N—CH₃.
 12. The process as claimed in claim 1,wherein the copolymerization of stage (ii) is carried out in thepresence of a chain-transfer agent of thiol type.
 13. The process asclaimed in claim 12, wherein the chain-transfer agent is a silanolfunctionalizing agent.
 14. The process as claimed in claim 12, whereinthe transfer agent is an agent of formula HS-Ro-Si—(OR_(1a)), in whichR_(1a) is H or a saturated C₁ to C₃ alkyl group and Ro is a linear orbranched alkyl chain, or the said agent in mixture with H₃PO₂, H₃PO₃ orone of their salts.
 15. The process as claimed in claim 5 where m isgreater than
 20. 16. The process as claimed in claim 9 wherein the ratioby weight of monomer (1) to monomer (2) is between 50:50 and 98:2.